Evidence of Grammatical Knowledge in Apes: An Analysis of Kanzi's Performance on Reversible Sentences

Ape language acquisition studies have demonstrated that apes can learn arbitrary mappings between different auditory or visual patterns and concepts, satisfying the definition of symbol use. The extent to which apes understand aspects of grammar is less well accepted. On the production side, several studies have shown that apes sometimes combine two or more symbols together, in non-random patterns. However, this is quite limited compared to human language production. On the comprehension side, much greater abilities have been reported in apes. One of the most famous examples is Kanzi, a bonobo who reportedly responded correctly to a large number of novel commands. However, based on his performance on a small subset of reversible sentences-where the understanding of English syntax was critical-the extent to which he demonstrated grammatical knowledge has been questioned. Using a randomization study it is shown here that his performance actually vastly exceeds random chance, supporting the contention that he does in fact understand word order grammatical rules in English. This of course represents only one aspect of English grammar, and does not suggest he has completely human grammatical abilities. However, it does show that he understands one of the arbitrary grammatical devices used in many languages: The use of word order to code argument relations. It also removes from serious consideration the view that apes lack any kind of grammatical ability. From an evolutionary perspective, Kanzi's ability is most likely to result from homologous brain circuitry, although this is ultimately an empirical question.

Automated summary

Studies on ape language acquisition have shown that apes can learn to use symbols to represent concepts, although their understanding and production of grammar is more limited compared to humans. Some apes have been observed to combine symbols in non-random patterns, but this ability is still not as extensive as human language production. However, apes have shown greater comprehension abilities, with examples like Kanzi, a bonobo, who has responded correctly to novel commands. However, his understanding of grammar has been questioned based on his performance with reversible sentences. A randomization study has supported the contention that Kanzi does understand word order grammatical rules in English.